1. Field of the Invention
The present invention relates to a liquid chromatograph having a trapping column for analyzing a dilute sample through concentration.
2. Description of the Related Art
In relation to a high-performance liquid chromatograph, when a sample is injected into an injection port, the thus-injected sample is usually sent to an analysis column by means of a mobile phase sent by a liquid delivery pump, and the sample is separated by the analysis column. When the sample injected into the injection port is of large quantity, a band of the sample in the analysis column is broadened by action of a solvent contained in the sample, so that the separation performance of the analysis column is reduced, thereby posing difficulty in highly-sensitive analysis. However, in the analysis of a diluted sample, a large quantity of sample must be injected in order to increase the absolute quantity of sample during analysis. In such a case, analysis is usually carried out by means of online concentration using a trapping column.
FIG. 5 is a flow passage diagram showing an example liquid chromatograph, wherein FIG. 5A shows an online concentration flow passage, and FIG. 5B shows a direct analysis flow passage.
As shown in FIG. 5A, in analysis involving concentration of a sample, a mobile phase solvent 5 is sent by a pump 10, thereby eluting the sample injected into the flow passage by an automatic sampler 18, and the thus-eluted sample is sent to a trapping column 20 via a switching valve 16. The sample is trapped in the trapping column 20, whereupon the sample is concentrated. After concentration of the sample, mobile phases 2a, 2b for analysis purpose are sent to a mixer 22 by analysis pumps 8a, 8b. The composition of the mobile phase is adjusted by controlling the flow rate of each of the analysis pumps 8a, 8b, to thus enable a gradient analysis. The mobile-phase solution mixed by the mixer 22 is sent to the trapping column 20 via the valve 16, thereby eluting the sample trapped by said trapping column 20 and sending the eluted sample to an analysis column 24. The sample is separated on a per-composition basis by the analysis column 24, and the thus-separated sample is detected by a detector 26.
In the direct analysis not involving concentration, the sample is injected to a position downstream of the mixer 22 directly from the automatic sampler 18, as shown in FIG. 5B. The sample injected into the flow passage is sent to the analysis column 24, where the sample is separated on a per-composition basis. The thus-separated compositions are detected by the detector 26.
In order to examine the concentration efficiency of the trapping column and deterioration of the column by means of online concentration analysis using the trapping column, identical samples were subjected to analysis using the online trapping column and analysis using the ordinary analysis column, and the results were compared with each other, to thus measure a recovery rate. In order to measure the recovery rate, the related-art liquid chromatograph was subjected to a change from (A) the online concentration flow passage to (B) the direct analysis flow passage. Operation for changing the plumbing is very complicated, and involves consumption of much time and consideration for prevention of leakage which would otherwise arise after changing of the plumbing; particularly, a dead volume in the plumbing for which micro flow rate or nano flow rate is critical.